TEETH OF MONOPHYODONTS. 279 



hollow bases inclosing the nncalcified remains of a vascular pulp. 

 In the foetus of a Balcenoptera, the jaws of which were about 

 four inches in length, the groove of the upper jaw contained 

 twenty-eight such teeth, that of the 

 lower jaw forty-two : these disappear 



before birth. The foetal Whale exem- £^\ £~\ jQ 

 plifies the earliest stage of dental de- jjfff wif yjj/ 

 velopment in the higher Mammals, Transltorj -denticles of Fcetaiwhaie 

 retaining the open fissure which in **.*■. 



them is rapidly closed. 



The great Bottle-nose or bident Whale offers a transitional 

 grade between the true Whales and the typical Delphinida. The 

 foetal denticles do not all perish, but two or three of the anterior 

 pairs acquire a large size as compared with their transitory repre- 

 sentatives in the Balcenida — and one of these pairs is long retained 

 in the lower jaw, though functionless, and hidden by the gum. 



In the Narwhal (Monodon monoceros), two of the primitive 

 dental germs at the forepart of the upper jaw proceed in their de- 

 velopment to a greater extent than do those in the lower jaw of the 

 Hyperoodon ; but every other trace of teeth is soon lost. The two 

 persistent matrices rapidly elongate, but in the retrograde direc- 

 tion, forming a long fang rather than a crown ; each tooth sinks 

 into a horizontal alveolus of the premaxillary bone, or, rather, at 

 the junction of the premaxillary with the maxillary, and soon, by 

 the forward growth of these bones, becomes wholly inclosed, fig. 

 220, a, like the germs of the teeth of higher Mammals at their 

 second stage of development. In the female Narwhal, the pulp is 

 here exhausted, the cavity of the tooth is obliterated by its ossi- 

 fication, further development ceases, and the two teeth remain 

 concealed as abortive germs in the substance of the jaws for the 

 rest of life. In the male, the matrix of the tooth in the left pre- 

 maxillary, ib. b, continues to enlarge ; fresh pulp-material is pro- 

 gressively added, which by its calcification elongates the base, 

 protrudes the apex from the socket, and the tusk continues to 

 grow until it acquires the length of nine or ten feet, with a basal 

 diameter of four inches. This is that famous i horn ' which figures 

 on the forehead of the heraldic unicorn, and so long excited 

 the curiosity and conjectures of the older naturalists, until 

 Olaus Wormius made an end of the fabulous * monocerologies ' 

 by the discovery of the true nature of their subject. 1 



1 clx". Linnasus has embalmed the old idea of this weapon in the binomial 

 Monodon monoceros, under which the Narwhal is entered in the Systema Natures. 



